this invention relates generally to devices generating images of contact (such as fingerprints), and more specifically to a device that causes a pattern of contact itself to selectively close an open circuit, where such closure of the circuit energizes an irradiated image directly in register with the contact pattern.
Devices are known in the art to capture images described by contact on a surface. A primary, although by no means exclusive, application for such imaging devices is in the area of fingerprinting, whether for security, forensics or other purposes. Other applications include analysis of surface texture for classification or testing purposes, or recording contact for archival purposes, or possibly mechanical duplication.
All of the foregoing applications involve translating the image described by contact into a reproducible record of the image. For example, in the fingerprint application, a time-honored system is to xe2x80x9cinkxe2x80x9d the fingers and roll them on a paper or card surface. Of course, without further scanning of the results, such systems lack the capability to generate computer-ready signals representative of the images. Without the storage and analysis capabilities of a computer, cataloging and comparison of such fingerprint images is a time-consuming and unpredictable task.
More recent devices shine light onto the fingerprint via a prism. The reflected image may be captured on photosensitive film, or received onto a photosensitive array. In the latter case, the image may then be pixelated and stored as an analog or digital signal representative of the image. These signals are now available for further processing by computers.
The prior art references cited with this disclosure demonstrate that fingerprinting is a popular application of the xe2x80x9creflected imagexe2x80x9d technique. The same xe2x80x9creflected imagexe2x80x9d technique is also known to be used to scan paper or other textile images into scanners and photocopiers.
The disadvantage with all devices employing a xe2x80x9creflected imagexe2x80x9d technique of recording images is that by definition they need an independent light source and optical structure (such as a prism) to create a reflected image. The same is true of xe2x80x9creflected imagexe2x80x9d techniques using radiation outside the visible light band of the electromagnetic spectrum. By definition, an independent radiation source and reflective/diffractive structure is still required.
Other current art devices generating images by contact use proximity sensors to detect changes in characteristics such as capacitance or magnetic flux. The disadvantages of these devices are that (1) they can be unreliable, and (2) they can be costly. They are unreliable inasmuch that in detecting variations in, say, capacitance, there is no way to know whether capacitance change is caused by contact or by some other stray source. Further, an expense must be incurred in such devices in creating sensor circuitry having fidelity and resolution comparable to the capability of capturing and resolving reflected radiation such as visible light.
There is therefore a need in the art for a device generating images described by contact, where the contact is the primary source of energy for the image itself. In this way, the extra structure required in xe2x80x9creflected imagexe2x80x9d techniques would be obviated. Further, it would be highly advantageous if such an inventive device did not rely on proximity sensors to detect the contact. The inventive device would then have increased predictability in performance, without requiring complex sensor circuitry to interpret the contact.
These and other objects, features and technical advantages are achieved by an invention that generates images described by contact, in which the contact itself closes an open circuit to generate radiation in a pattern in register with the contact. In this way, an irradiated image results, which corresponds directly to the contact pattern energizing the radiation.
The invention thus has immediate (although not exclusive) application to fingerprinting techniques. In a preferred embodiment enabled by an electroluminescent system without a back electrode, a fingerprint is disposed to close the open circuit by making contact and thereby serving as a xe2x80x9ctemporaryxe2x80x9d back electrode. The electroluminescent system then energizes in a pattern in register with the contact (i.e. the fingerprint) to emit a high-resolution image of visible light with high fidelity to the contact. This image may then be directed on to a photosensitive array standard in the art suitable for pixelation and conversion into an electrical signal representative of the image. This signal is available for computerized storage, analysis, processing and comparison.
Advantageously, the electroluminescent system enabling a preferred embodiment is a low cost, screen-printed polymer thick film (xe2x80x9cPTFxe2x80x9d) lamp, which may be electrically powered at a low AC voltage (say 20-30 volts AC) at frequencies in a range of 400 Hz to 2 kHz. Such a power supply is well known in the art to be available from low voltage integrated circuit inverters (say 3-5 volts DC). The electroluminescent system will then be very safe to the touch by virtue of the very low current levels generated by such an electrical system.
Of course, it will be appreciated that the invention is in no way limited to fingerprinting applications. According to the invention, any form of electrically conductive contact will describe an irradiated image. Thus, the surface textures of many objects, animate or inanimate, may be imaged with the invention.
Further, the invention is not limited to contact generating visible light via electroluminescence. Although the preferred embodiment as described is highly advantageous, the invention in its broadest form encompasses generating irradiated imaged described by contact, where the contact itself closes an open circuit to energize radiation in register with the contact. Thus, generation of any radiation in the electromagnetic spectrum falls within the scope of the invention. For example, an infrared image could be generated by an open circuit where heat is emitted in pattern in register with selective closure of the circuit by the contact. Clearly, yet further fidelity and resolution of images described by contact may be available through selection of the wavelength of the radiation generated by the invention, as may be compatible with the device receiving and interpreting the irradiated image.
Similarly, the use of electroluminescence in the preferred embodiment should not be considered as limiting. Clearly, using the contact to form the back electrode of an electroluminescent lamp is a highly advantageous enablement of radiation in register with contact. The invention, however, is broad in concept in that it uses the contact itself to close an open circuit to energize radiation in register with the contact. Thus, it will be appreciated that the invention is enabled by any open circuit capable of generating radiation in register with selective closure of the circuit by a pattern of contact.
It is therefore a technical advantage of the present invention to generate an irradiated image corresponding to contact, by causing the contact to close an open circuit, thereby obviating the need for additional apparatus such as an independent radiation source and reflective/diffractive structure to enable a xe2x80x9creflected image.xe2x80x9d
It is a further technical advantage of the invention to eliminate the unpredictability and potential manufacturing complexity of devices using xe2x80x9cproximity sensorxe2x80x9d structure to generate an image of contact.
A yet further technical advantage of the invention is that it can be enabled reliably and economically on a screen-printed PTF electroluminescent lamp, where the contact forms the back electrode of the lamp. Visible light in a pattern in register with the contact may then be radiated towards a photosensitive array. This array in turn may pixelate the image and prepare a computer-ready signal corresponding to the image.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.